The MRI apparatus is an image diagnostic apparatus which magnetically excites nuclear spins of a subject set in a static magnetic field with a RF (radio frequency) signals having the Larmor frequency and reconstructs an image based on NMR (nuclear magnetic resonance) signals generated due to the excitation.
The MRI apparatus includes a cylindrical WB (whole body) coil as a transmission RF coil which applies RF pulses to the whole imaging region. The WB coil is fixed to the gantry and it is not assumed that a user removes the WB coil. On the other hand, a local transmission RF coil which transmits RF pulses to a desired and restricted imaging region locally can be used for imaging. When a local transmission RF coil is used, the power consumption can be reduced and an RF magnetic field having a larger intensity can be generated with little electric power.
The local transmission RF coil is sent in the gantry with a subject in the state where the local transmission RF coil has been attached to the subject set on the bed. Thus, the local transmission RF coil is connected with the control system of the MRI apparatus via a connector. Then, the local transmission RF coil is used in the state where the local transmission RF coil has been arranged inside the WB coil.
In many MRI apparatuses, it is recognized by connecting a local transmission RF coil to a connector in an MRI apparatus side that the local transmission RF coil can be used. Furthermore, the WB coil which is an RF coil for transmission is electrically broken when a connection of a local transmission RF coil is recognized by the system of an MRI apparatus side. Thereby, electric coupling between the local transmission RF coil and the WB coil is avoided.
Note that, many local transmission RF coils also have the function to receive NMR signals. Examples of local transmission/reception RF coil having the reception and transmission function of signals include a local transmission/reception RF coil for head and a local transmission/reception RF coil for knee. As a typical local transmission RF coil, a birdcage type of RF coil is known. The birdcage type of RF coil is a coil which is made by connecting two rings by rungs.